1. Field of the Invention
The present invention relates to dual channel control systems and, more particularly, to dual channel control systems having improved channel equalization which permits the tightening of system monitor thresholds without causing nuisance failure warnings or disengagements.
2. Description of the Prior Art
Dual channel servo control systems are known in the prior art and one type thereof incorporating duplex differentially combined servomotors is exemplified by the system described in Applicant's assignee's pending U.S. Patent Application Ser. No. 811,653 entitled "Fail Passive Dual Servo with Continuous Motor Speed and Acceleration Monitoring", by M. P. DeWalt, filed June 30, 1977 and Applicant's assignee's U.S. Pat. Nos. 3,504,248 and 4,035,705, entitled "Dual Channel Servo System Having Torque Equalization" and "Fail Safe Dual Channel Automatic Pilot with Maneuver Limiting", respectively, issued on Mar. 31, 1970 and July 12, 1977, respectively, both by H. Miller. However, the present invention is also applicable to more conventional dual channel autopilots. For example, well known dual channel flight control systems utilizing differentially coupled hydraulic actuators.
The primary characteristic of the dual channel control systems is that the dual channel control actuators or motors must track each other in velocity and direction to accurately control the position of the output member such as a control surface in response to a commanded input. Such systems, no matter how carefully designed, may be subject to undesired spurious signals due to inherent servo amplifier unbalance, differences in signal output gradients and nulls of the various sensors in response to command signals, and other tolerance differences between the two channels.
In addition, it is noted that in such control systems, particularly of the duplex electromechanical differentially summed output type, the degree of unbalance may be of such magnitude as to result in full speed output of the motors in opposite directions with respect to each other, resulting in total loss of control authority of the system. Velocity equalization is also known in the art, such as the electrical equalization described in said U.S. Pat. No. 3,504,248, which may be utilized to provide an equalization signal, having set limits, to each channel such that the dual channel actuators track each other reasonably well and thereby provide adequate control authority. However, the monitor circuits of such prior systems must be sufficiently loose as to induce nuisance trips during large control commands, non-limitations and component tolerances.
Accordingly, as the velocity differential between the actuators, e.g., electromechanical or hydraulic actuators, may increase for large surface commands due, for example, to the position feedback synchro gradient mismatch, the velocity equalization may be subject to transient signals of magnitude greater than the velocity equalization fixed limits, resulting in nuisance monitor trips.